1 accident
On February 16, XXXX, a generator trip occurred in a power plant. The accident occurred as follows:
At 10:55, the value is long and the provincial adjustment is required. The No. 2 machine is required to perform vibration and swing measurement under various working conditions before the unit minor repair. After the provincial agreement was approved, at 11:06, the No. 2 machine was turned on and successfully connected to the network. At that time, the plant operated as follows:
220 kV double mother operation, No. 1 machine with 60 MW to 220 kV Jiamu, No. 2 with 60 MW to 220 kV mother, the total power of the whole plant is 120 MW. The main transformer cooler mode is: No. 1 cooler is in the working position, No. 2 cooler is in the auxiliary position, No. 3 cooler is in the standby position, and No. 4 cooler is in the stop position. The No. 2 main transformer cooler is powered by I.
At 12:02, the buzzer sounded, the electric bell rang, and the 2202 switch tripped, causing the No. 2 machine to stop.
2 Analysis of the cause of the accident
After the accident, the operator checked the equipment. In the protection screen next to the machine, it is found that the main transformer cooler of the B cabinet is completely stopped, and the lights of No.1 and No.2 are on; the indicator lights of the A, B, and C phases of the C cabinet are on, and the other indicators are not abnormal; the main body of the No. 2 main transformer has no abnormality, the main change The oil temperature is normal (34 °C), the power supply monitoring indicator of the main transformer cooling control cabinet is 1XD off, 2XD is on, and 4 cooling fans are in the stop condition. Further inspection reveals that the 1RD fuse of the operation circuit is blown; the integrated screen of the central control room is No. 2 The electrical sign of the machine is bright, and the signal screen "No. 2 machine cooler is fully stopped" is illuminated.
Immediately afterwards, the relevant personnel were organized to investigate and analyze the accident. The main causes of the accident were:
(1) Unit 11 at 11:05 is connected to the grid and operated according to the order. Because the No. 2 main transformer cooler circuit breaker 1RD (5A) is blown, the main converter cooler stops, causing the No. 2 unit to start after 60 minutes. The variable cooler is fully stopped to protect the action, causing the 2202 switch to trip and the No. 2 unit to stop.
(2) The operating personnel did not send a protective screen to the machine side to check and reset the signal after the power was turned on for 60 minutes; no one was sent to the main transformer cooling control cabinet to check the power monitor light and observe the main transformer cooling. The operation of the fan is an important cause of the accident.
(3) After the fuse of the main transformer cooler is blown, the original design wiring of the control loop is not reasonable, which causes the automatic switching function of the I and II segments of the cooler to fail. The contactors 1C and 2C cannot be used. Closing, causing the main transformer cooler power to stop. This is the direct cause of the accident.
3 Improvement measures
The lesson of this accident is extremely profound. It reveals that there are many weak links in the safety management of the plant. For example, the personnel are paralyzed, the safety awareness is not strong, the management work is not deep, not fine, not strict, and there is no good work. Style and a high degree of safety responsibility. In addition, there is one more direct reason, that is, the control loop has serious defects. There is a workable way to eliminate the above drawbacks.
First, a pair of closed points of the original circuit are introduced into the central control room signal screen. When the mains cooler load side AC power is lost, the "main transformer cooler power failure" signal is turned on by the pair of closed points to serve as a reminder to the attendant.
At the same time, by changing the control loop, adding two time relays in the loop and changing the original intermediate relay to a voltage relay to complete the automatic switching function of the coolers I and II. When the fuse is blown, the time relay is demagnetized, the voltage relay acts, and its normally open contact is closed, so that one of the contactors is excited, and the two contactors (1C, 2C) are switched to each other, and the standby working power circuit is also It is automatically put into operation. The problem of not being able to automatically switch is fundamentally eliminated, and the sensitivity and reliability of the secondary loop are improved.
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